Compact Wheel Coupler

Wow! Given the complexity of the motor mounting block on the previous page and the compact coupler on this page, it is no wonder that Yummy took much longer to build than expected.

The wheels on the m&m’s Beetle candy tin are attached by aluminum rivets; allowing the wheels to spin freely.
The rivets can be removed by squishing the inner head (shop head or buck-tail) with pliers.

Views of a rivet outside, inside, and removed

To provide motion, the motor needs to be connected to the wheels somehow.
This is called a coupler.
I’ve created a large variety of couplers over the years, but primarily to mate with a Lego wheel.
The coupler for this robot has many similarities to a Lego coupler, but doesn’t include space for a cross axle as the wheel sits directly on the coupler itself.

The length of the output shaft on the Faulhaber motor drive box is quite reasonable, at around 8 mm.
The apparent width of the candy-tin wheel is 2.5 mm, but actually closer to 4 mm when accounting for the inner embossed portion that simulates a hub.
In any case, although a longer coupler would be easier to make and attach, it would stick out and be unsightly.
I chose to create a coupler that is short enough to be unnoticed when compared to the original rivet.

The wider end of the custom coupler has a pair of offset setscrews to securely hold onto the motor shaft.
The wider end is on the outside of the wheel.

Custom coupler connects motor to stamped metal wheel

The narrower middle section fits inside the hole in the wheel.
The tapered end provides some support in keeping the coupler straight against the motor shaft while not rubbing against the hole in the candy-tin body where the original rivet rested.

Aluminum coupler replaces rivet on toy wheel

The coupler can be secured to the metal wheel with some adhesive.
I was fortunate enough to get a near friction fit by machining the diameter of the coupler to the same size as the wheel rivet hole.

Making the Coupler

The coupler is made out of aluminum on a lathe.
The first step is to reduce the rod’s diameter to fit the hole in the wheel.
Then, a hole is drilled to fit the 3 mm motor shaft.

Reducing diameter and drilling center of a rod on a lathe

Next, the wheel is placed onto the rod to eyeball an acceptable amount of overhang.
The wheel is removed before machining off the excess rod.

Checking wheel diameter and cutting off excess rod

The motor shaft is placed beside the rod to determine the final length of the coupler.
Normally, I would have performed more precise measurements, but only two couplers are being created and they are relatively simple.

Marking coupler length before cutting from rod

The coupler is cut off from the rod with a cut-off blade.
(I should have used a live or dead center to support the free end of the rod during cutting. Sorry about that.)

Cutting coupler from rod with a cut off blade

Lastly, the setscrew holes are drilled on a v-groove vise on a milling machine or drill press.
2-56 screws are used.

Drilling setscrew hole in V-groove vise

Wave Goodbye

Yummy turned out well. I like the...

Headlights

Taillight lenses

Lack of Lego wheels to retain original appearance

Blue rubber band tires

Yummy waving goodbye

I wish I had...

Some way of preserving the rubber bands. They are going to crumble and fall off years from now

Added sound

Hidden the floor sensor board inside the body

Installed a pushbutton underneath the robot, so that the tin wouldn’t need to be opened and closed